In steam generating systems such as various industrial processes or plants, for example, power plants, an air cooled condenser is employed downstream of a steam turbine to convert steam, after it has passed through the steam turbine, from its gaseous state to its liquid state. One of the most wide spread dry cooling systems employed is the direct dry cooling. In this cooling method, if it serves power plant cycles, the water vapor, expands in a steam turbine, exits from the turbine through a steam pipe with a large diameter, then through an upper distribution chamber where it enters a steam-air heat exchanger such as an air cooled condenser.
During operation, the steam flows into the condenser. As previously mentioned, the condenser may be air-cooled and comprises a steam inlet duct, a plurality of condenser tubes, and a condensate outlet duct. Steam passes into the condenser through the steam inlet duct and flows through the condenser tubes. Air is forced over outer surfaces of the tubes so as to cool the tubes and, hence, the steam flowing through the tubes, thus causing the steam to be converted into a liquid condensate. The condensate can be reused in generating steam for the steam turbine such that at least a portion of it later returns to the condenser where it is once again is converted to its liquid state in the condenser.
During the start-up operation of a power plant or the like, steam is slowly introduced into the air cooled condenser (ACC) due to the start up “behavior” of the boiler used in such systems. It is desirable to avoid backpressure peaks in order to have safe operation of the steam turbine. Due to the large volume of air trapped in the air cooled condenser (ACC) system prior to start up, a pressure peak can occur due to the compression of the trapped air inside air cooled condenser (ACC). Typically, the volume of trapped gas is such that the backpressure peak normally happens when steam has not yet arrived at the exchange tubes, but upon initial start up procedures. Moreover, because the air cooled condenser pressure is typically below atmospheric pressure, it is not possible to employ a valve to vent to entire system while injecting steam therein during start up.
One solution to the aforementioned problem is to increase the air ejection equipment capacity which can more rapidly reduce the amount of air trapped in the air cooled condenser (ACC) which will in turn reduce the potential for a backpressure peak. Nevertheless, this solution can lead to drastic cost increase of as it may require significant capital investment as the air extraction equipment is expensive and has to be adapted to the air cooled condenser (ACC) configuration and process daring start up conditions.
Accordingly, it is desirable to provide a steam turbine system employing an air cooled condenser that is economical and safe during start-up procedures. More specifically, it is desirable to provide an air cooled condenser design and method of start up that isolates some of the volume of the trapped air in the air cooled condenser system that is economical and safe.